Venous supply to brain:Venous sinuses
Dural venous sinuses are venous channels located intracranially between the two layers of dura mater (endosteal layer and meningeal layer). They can be conceptualised as trapped epidural veins. Unlike other veins in the body they run alone, not parallel to arteries. Furthermore, they are valveless, allowing for bidirectional blood flow in intracranial veins. It is also important to note that the draining territories of intracranial veins are different from those of major cerebral arteries. Together the dural venous sinuses form the major drainage pathways from the brain, predominantly to the internal jugular veins. The main dural venous sinuses are: Unpaired * Superior sagittal sinus: the largest dural venous sinus. ** runs in a sagittal plane from the anterior aspect of the falx cerebri to its termination at the confluence of sinuses at the occipital protuberance ** Terminates at venous sinus confluence (often runs off toward right transverse sinus) ** Important hemispheric tributary: cortical veins including Vein of Trolard. * inferior sagittal sinus: ** runs in inferior (free) margin of falx cerebri ** lies above corpus callosum, from which it receives tributaries ** terminates at falcotentorial apex, joining with vein of Galen (VofG) to form straight sinus * straight sinus: ** runs through the junction between the falx cerebri and the tentorium cerebelli ** It receives the inferior sagittal sinus, the vein of Galen at its anterior end and some superior cerebellar veins along its course, and runs posteroinferiorly towards the confluence of sinuses. * occipital sinus: the smallest of the dural venous sinuses and lies on the inner surface of the occipital bone. Tributaries from the margins of the foramen magnum, such as the sigmoid sinus and internal vertebral plexus, coalesce to pass in the occipital sinus within the attached margin of the falx cerebelli to drain postero-superiorly at the confluence of the sinuses. * intercavernous sinus: anterior and posterior, are dural venous sinuses and connect the left and right cavernous sinuses, along with the basilar sinus (plexus). They lie in the anterior and posterior borders of the diaphragma sellae. Additional small venous sinuses in the base of the pituitary fossa drain into the intercavernous sinuses, and are a cause of bleeding during transphenoidal hypophysectomy. Paired * Transverse sinus ** Contained between attachment of tentorial leaves to calvarium ** Extends laterally from occiput to posterior border of petrous temporal bone, receiving tributaries from tentorium, cerebellum, inferior temporal/occipital lobes. ** Often asymmetric (right side usually larger than left) ** Important tributary: Vein of Labbé * sigmoid sinus: ** anteroinferior continuation of the transverse sinus from the ending of tentorium. ** Receives the superior petrosal sinus. ** It passes inferiorly in an S shaped groove posteromedial to the mastoid air-cells to the jugular foramen and end in the jugular bulb, in pars vascularis. * inferior petrosal sinus: ** runs long petrooccipital fissure from clival venous plexus to the jugular foramen. ** drains blood from the cavernous sinus to the jugular vein. * superior petrosal sinus: ** drains the cavernous sinus, posterolaterally to the transverse sinus. ** runs along superior aspect of the petrous temporal bone. ** receives cerebellar veins, inferior cerebral veins, labyrinthine vein draining the inner ear structures. * cavernous sinus * sphenoparietal sinus * basilar venous plexus Confluence of sinuses: The confluence of sinuses, also know as torcula Herophili, is the site of confluence of: * superior sagittal sinus * straight sinus * occipital sinus * transverse sinuses The anatomy is highly variable and three types can be distinguished: * type 1: superior sagittal sinus drains into one lateral sinus and the straight sinus into the other, with no connection between the two * type 2: superior sagittal sinuses and the straight sinus fork, and the forks from both sinuses join to form the lateral sinuses * type 3: true confluence of sinuses Communication: * Communicate with extracranial veins directly (via diploic veins in calvarium, emissary veins through basilar foramina) * Receive venous blood from superficial (cortical) veins, deep (subependymal) veins Normal Variants, Anomalies * Common variants ** Absent anterior SSS (may begin posteriorly near coronal suture) ** "Off-midline" SSS terminating directly in TS ** Absence or hypoplasia of part/all of TS ** Jugular bulbs can vary greatly in size, configuration (can be "high-riding", have jugular diverticulum, dehiscent jugular bulb) ** "Giant" arachnoid granulations (round/ovoid CSF-equivalent filling defects in dural sinuses) * Anomalies ** Persistent embryonic falcine sinus (usually with VofG malformation) ** Lambdoid-torcular inversion with high sinus confluence (with Dandy-Walker spectrum)